For the generation of 3D video content it is important to measure the distance of objects located in a scene that is being captured in addition to the usual video data. For this purpose a so-called depth map is determined. Typically a time-of-flight imager is used for this purpose, i.e. a measurement system that creates distance data with help of the time-of-flight principle. The time-of-flight imager includes a light source and a light sensor, which consists of an array of pixels. To measure a depth map, the light source is triggered with a pulse, and all pixels of the sensor are simultaneously triggered with a Transfer Gate (TG) pulse and a Global Shutter Gate (GSG) pulse. For details see K. Fife et al.: “A 0.5 μm pixel frame-transfer CCD image sensor in 110 nm CMOS”, 2007 IEEE International Electron Devices Meeting, Vol. 35 (2007), pp. 1003-1006.
Also, WO 2009/135952 discloses methods and sensors for time-of-flight measurements. The sensors are adapted to achieve efficient background radiation suppression at variable background radiation conditions.
Not only background radiation reduces the accuracy of the depth map measurement. To obtain an accurate depth map it is likewise important that the temporal relations between the light source, the transfer gate pulse and the global shutter gate pulse are constant.